Audio-electric translating device



Oct. 18, 1960 G. D. CHICHESTER AUDIO-ELECTRIC TRANSLATING DEVICE FiledFeb. 21, 1956 FIG. I

' GEORGE D cHlc fl s FIG. 2 By flaw rm AUDIO-ELECTRIC TRANSLATING DEVICEGeorge D. Chiehester, Pittsburgh, Pa., assignor to General PhonesCorporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. 21, 1956, Ser. No. 566,961

9 (Ilaims. (Cl. 179-114 This invention is for an audio-electrictranslating device applicable for use either as a device for convertingelectric impulses into sound, as for example a loud speaker, or forconverting audible vibration into electric impulses, that is, amicrophone.

My invention has for its object to provide a device of this character inwhich permanent magnets are used, with the magnets and related partsbeing more effectively arranged than heretofore to respond over a widerrange of audio frequencies and secure high fidelity reproduction with awide range of volume or amplitude.

A further object of my invention is to provide a device of this kind inwhich superior results are achieved with a reduction in the mass of thepermanent magnets, not only reducing distortion due to inertia, butsubstantially reducing the cost.

A further object of my invention is to provide a device of thischaracter in which good response is secured with higher impedance in thearmature coil than may now be practically provided, better suiting theimpedance of the speaker to other components of the circuit in which itis used.

These and other objects and advantages are secured by my invention whichmay be more fully understood by reference to the accompanying drawings,in which:

Fig. l is a transverse section through a cone speaker embodying one formof my invention;

Fig. 2 is a vertical section on a larger scale than Fig. l, of aslightly modified construction; and

Fig. 3 is a transverse section through a still further modification.

In the drawings, 2 designates the parchment paper cone of customaryconstruction as used in a loud speaker, and 3 designates the ring aroundthe periphery of the cone providing the mounting for the cone in ahousing (not shown). At the center of the cone is a soft iron ormagnetizable disk 4 which is frequently made with a peripheral flange 5to which the center portion of the cone is attached, and the center ofthe disk 4 may have a small button-like protuberance 6 embossed therein,but this is not necessary. Cemented to one face, preferably the rearface of the disk 4 around the central button 6, is a fine wire windingor hollow coil of disk-like form designated 7, and which is providedwith lead wires 8 and 9, the convolutions of the coil being in planes atright angles to the axis'of the coil, in the conventional manner.

With the present invention there are provided two small but powerfulpermanent bar magnets 10 and 11. High magnetic alloy metal is preferablyused for these materials. typical of which is the metal(aluminum-nickelcobalt alloy) sold under the trademark Alnico. The twobar magnets 10 and 11 are placed in aligned confronting relation to eachother with similar poles opposed. For example the two north poles are inconfronting relation and separated from each other by a very small airgap. These confronting poles tend of course to repel each other, butthey are held in fixed rela- Patented Oct. 18, 1960 tion to one anotherby a core or button 12 of soft iron which may be welded to them, orotherwise permanently secured to keep the bar magnets in fixed position.The free end of this button or pole piece 12 is of a diameter such as tofit into the central opening of the coil 7. It terminates with the endat about the level of the rear face of the coil, or with the endprojecting a very small fraction of an inch into the coil. It is mosteffective if it just barely enters the coil, although this is not anecessary condition.

This magnet assembly as shown in Fig. 1 is held in spaced relation tothe coil by resilient blocks 13 of rubber, resilient silicone resin, orother compressible resilien-t material. The blocks 13 may be cemented tothe rear face of the coil 7, and the magnet bars 10 and 11 may havefiber strips 14 adhered to their inner surfaces, which are in turncemented to the outer faces of the blocks 13. On the outer faces of thebar magnets 10 and 11 there may be other strips 15 of non-magneticinsulating material to which there is cemented a magnetizable metal diskor connecting plate 16 which serves also to hold the parts in assembledrelation.

The lines of force emanating from the opposed poles N of the bar magnets10 and 11 of course tend to repel each other and deflect them from theirnormal field, so that the lines of force pass through the button 12'andemerge from the face of this button creating a very strong magneticattraction between the face of the button 12 and the center of he disk4. The field is thus made strongly effective in a plane perpendicular tothe plane of the bar magnets. The pole piece or button 12 thus becomes acommon pole piece, the polarity of which is opposite the polarity of thetwo remote ends of the twobar magnet assembly.

Minute variations of current flowing through the coil 7 react with oragainst the field projected from the pole piece 12, either increasing ordecreasing the efiect of the field. An increase in the effect of thefield tends to compress the blocks 13 and create relative movementbetween the magnet assembly and the diaphragm. A magnetic fieldgenerated by the coil opposing the field of the permanent magnet ofcourse has the reverse effect and tends to create relative movementbetween the diaphragm and the magnet away from each other.

In the conventional apparatus of this kind the permanent magnet normallyhas its axis perpendicular to the diaphragm, and the lines of force fromthe pole piece extend in a more or less normal pattern, whereas in thepresent invention the. mutually repugnant fields of the two magnets areboth projected into and from the end of the common magnetizable button12, creating an entirely different relation between the field and themagnetic coil than has heretofore been provided. Because of thisrelationship the device will respond with higher fidelity over theentire audible range, and respond to more minute variations of currentwith far less amount of metal in the permanent magnets than hasheretofore been considered practical. Not only does the translatingdevice as thus constructed respond with greater fidelity over a widerrange of audio frequencies, but I have determined that the impedance ofthe coil 7 may be increased substantially over the impedance permittedwith speakers of present design. This increases the fidelity of thereproduced sound because the impedance of the speaker can be moreclosely conformed and adjusted to-the impedance of other elements in thecircuit in which the device is used, than has heretofore been practical.

The arrangement shown in Fig. lris satisfactory for speakers in a lowerprice class, but for microphones and better quality speakers, the

construction. shown in Fig. 2 I

In this construction, 20 designates a disk similar to disk 4, and it maybe flat as shown, or have an outwardlyembossed center area as in Fig. 1.It is shown with a peripheral flange 21, but this need not be provided.There is a disk-like open-center or hollow coil 22 corresponding to coil7 mounted on the disk. The permanent magnet assembly comprises two barmagnets 23 and 24 disposed as in Fig. l with their like poles inconfronting closely separated relation, and a magnetizable soft iron orlike button 25 is joined to them, as in Fig. 1 and holds them in fixedrelation. A flanged sleeve 26 of insulating material is provided at therear face of the coil and the button 25 has a free working fit in theouter end of the sleeve, the button or armature just barely entering thecenter of the field coil.

Instead of being supported on the coil as in Fig. l, the permanentmagnet assembly is secured, preferably through a magnetizable body ordisk 27 insulated as is button 16 of Fig. 1 from the permanent magnets,to a supporting bridge 28 that is fixedly mounted in a housing (notshown). In other words, the mounting more nearly resembles theconventional mounting used in devices of this general character.

My invention has been described particularly with reference to so-calledloud speakers, but is applicable to microphones. It provides anaudio-electric translating device characterized by the provision of twopermanent bar magnets in end-to-end relation with like poles inopposition and with the longitudinal axes of the bar magnets being atright angles to, or in a plane transverse to the longitudinal axis ofthe field coil. My invention increases the effectiveness of the opposedfields of these magnets by the provision of a pole piece of magnetizablematerial projecting from the confronting ends of the magnets to the endof the field coil where its effect or the electro-magnetic field of thecoil is at a maximum. The coil is of flat construction, so that evenwhen the coil is deenergized, the magnetizable disk on which the coil ismounted is infiuenced or biased by the field of the permanent magnet.

The small mass of the permanent magnets is not only a very economicaladvantage from the standpoint of cost, as is also the absence of closelymachined parts, but the low mass decreases the inertia and increasessensitivity. Much greater volume without blasting is also secured. As amicrophone of the electromagnetic type, it is highly satisfactory andappears to perform in a manner equal to or superior to much more costlymicrophones of other types, both as to sensitivity and fidelity.

In the modification shown in Fig. 3 the magnet assembly is substantiallythe same as that before described, but the coil instead of being placedon the armature disk, is placed on the magnetizable pole piece. In thisconstruction the bar magnets are designated 30 and 31. As heretoforedescribed, they are so positioned that their like poles are inconfronting relation. In this figure, however, the magnetizable polepiece 32 is shown as having a small extension 33 that is interposedbetween these confronting ends of the magnets. The coil 34 is positionedaround the magnetizable pole piece 32 and has its inner face restingagainst the magnets 30 and 31. The lead wires to the coil are designated35. The magnets in addition to having their ends secured to the polepiece 32 are mounted on a non-magnetic disk 36 which may be made ofinsulating material such as plastic. The disk 36 is supported at itsperiphery on a collar 37 which may be formed of plastic, or which may beof aluminum. A resilient gasket is preferably interposed between thedisk 36 and the collar 37.

The magnetizable diaphragm 39 is supported at its periphery on thecollar 37. The center of this disk is spaced a slight distance from themagnetizable core 32. All of the parts are cemented together so thatthere can be no free vibration. I have found that superior results canbe obtained by securing to the front of the disk a fiber collar 40. Thecollar 40 may be secured'to the dia-. phragm 39 by suitable cement. Thecollar 40 is in turn mounted on the support for the speaker which, inthe case shown in Fig. 3, constitutes the center portion of a cone 41.

It is to be noted that the fiber ring it? is spaced inwardly from theperiphery of the disk 39. The fiber ring 40 should be of suflicientlyless diameter than the collar 37 that the disk 39 will overhang thecollar 40 a substantial distance. As thus constructed it will be seenthat the collar 40 in a sense provides a fulcrum between the the centerof the disk which is attracted by the magnet 32 and the periphery towhich the magnet assembly is secured to the disk. The collar 40 not onlyprovides a support for the disk 39 intermediate its center and edge, outit also provides a sound throat which appears to improve the acousticalproperties of the speaker.

The speaker as thus constructed is easy to assemble and economical tomanufacture. By placing the coil 34 about the magnetizable pole piece 32instead of placing it on the armature as in the construction heretoforedescribed, it is possible to use a much larger coil and thereby increasethe impedance. One difliculty with speakers as heretofore constructedhas been the relatively low impedance which it has been possible tointroduce into the coil. By using a higher impedance in the coil it ispossible to eliminate the transformer between the last stage of theamplifier and the loud speaker, and thereby connect the speaker directlyinto the plate circuit of the last stage of amplification. This in turnallows a higher fidelity of reproduction and eliminates a part from thereproducing circuit. The speaker responds well over the entire normalaudible range, and while it will operate at a loud volume of soundwithout blasting, it is unnecessary to operate at great volume in orderto hear the bass notes. The bass notes will be distinctly audible eventhough the speaker is turned to a very low volume of sound.

While Fig. 3 shows the magnetizable pole piece 32 as having an extension33 interposed between the ends of the bar magnet, this construction isnot necessary and the arrangement shown in Figs. 1 and 2 may be used.Also the arrangement shown in Fig. 3 could of course be used in thedevices shown in Figs. 1 and 2. The use of the extension 33 on themagnetizable pole piece may have some advantage in assembly operationssince it will act as a spacer in positioning the magnet during theassembly of the speaker. The collar 46 may be used with the arrangementsshown in Figs. 1 and 2, but its use in Fig. 3 is especially desirablebecause of the cantilever elfect obtained by having the magnet assemblysupported on the periphery of the disk with the collar 40 inwardly fromthe periphery.

While I have shown and described certain specific embodiments of myinvention, various structural changes and modifications may be made inthe specific adaptation of it to its ultimate commercial form.

I claim:

l. An audio-electric translating device comprising a magnetizablediaphragm member, a magnetizable pole member having one end extendingtoward and terminating in spaced relation to one face of the diaphragmmember, a pair of bar magnets having ends of like sign in confrontingrelation with said ends positioned over that end of the pole memberwhich is remote from the diaphragm, the magnets being in a common planeperpendicular to the axis of the pole member, a coil mounted on one ofsaid members and located in the space between them, a supporting diskfor the bar magnets, a collar interposed between the periphery of thesupporting disk and the diaphragm and secured to the disk and thediaphragm, and means for supporting the diaphragm.

2. An audio-electric translating device as defined in claim 1 whereinthe coil surrounds and is mounted on the pole member.

3. An audio-electric translating device as defined in claim 1 whereinthe supporting means comprises a fiber sleeve concentrically positionedon that face of the diaphragm which is opposite the face confronting thepole member, the sleeve being smaller in diameter than the diaphragm andof less diameter than said collar interposed between the diaphragm andthe disk.

4. An audio-electric translating device as defined in claim 1 in whichthe bar magnets are mounted on a nonmagnetizable disk, the collar beinginterposed between the periphery of said disk and the periphery of thediaphragm and secured to both the diaphragm and the disk, a resilientgasket on the collar effective between the diaphragm and the disk whichsupports the bar magnets, and a second collar of less diameter than thefirst concentrically positioned on and secured to the opposite face ofthe disk.

5. An audio-electric translating device as defined in claim 4 in whichthere is a cone attached at its center to the second collar.

6. An audio-electric translating device of the class described having apermanent magnet assembly comprised of a pair of permanent bar magnetsin fixed endto-end position and with like poles in confronting relationbut with an air gap between them, a magnetizable button member on thefaces of the bar magnet at the confronting poles spanning the gapbetween them, a magnetizable diaphragm in a plane parallel to the planeof the two bar magnets and perpendicular to the axis of the button andspaced from that end of the button remote from the bar magnets but inclose proximity thereto and centered over the button, the magneticcircuit from the remote ends of the bar magnets being open and free ofany metallic conducting path from the plane of the bar magnets towardthe plane of the diaphragm, and a coil interposed between the diaphragmand the bar magnets concentric about the axis of the magnetizablebutton.

7. An audio-electric translating device of the class described having apermanent magnet assembly comprised of a pair of permanent bar magnetsin fixed endto-end position and with like poles in confronting relationbut with an air gap between them, a magnetizable button member on thefaces of the bar magnet at the confronting poles spanning the gapbetween them, a magnetizable diaphragm in a plane parallel to the planeof the two bar magnets and perpendicular to the axis of the button andspaced from that end of the button remote from the bar magnets but inclose proximity thereto and centered over the button, the magneticcircuit from the remote ends of the bar magnets being open and free ofany metallic conducting path from the plane of the bar magnets towardsthe plane of the diaphragm, and a coil interposed between the diaphragmand the bar magnets concentric about the axis of the magnetizablebutton, the coil being a flatttened coil carried on the diaphragm withone plane of the coil being in substantially the plane of the end of thebutton remote from the bar magnets.

8. An audio-electric translating device of the class described having apermanent magnet assembly comprised of a pair of permanent bar magnetsin fixed endto-end position and with like poles in confronting relationbut with an air gap between them, a magnetizable button member on thefaces of the bar magnet at the confronting poles spanning the gapbetween them, a magnetizable diaphragm in a plane parallel to the planeof the two bar magnets and perpendicular to the axis of the button andspaced from that end of the button remote from the bar magnets but inclose proximity thereto and centered over the button, the magneticcircuit from the remote ends of the bar magnets being open and free ofany metallic conducting path from the plane of the bar magnets towardthe plane of the diaphragm, a coil interposed between the diaphragm andthe bar magnets concentric about the axis of the magnetizable button,and resilient means holding the diaphragm in permanent magnet assemblyin the aforesaid relationship.

9. An audio-electric translating device having a diaphragm, a hollowcoil on the diaphragm, a permanent magnet assembly mounted adjacent thecoil and diaphragm comprising two separate permanent bar magnets withlike poles in closely spaced confronting relation, the magnets being ina plane transverse to the axis of the coil, a magnetizable pole piece onthe confronting ends of the two bar magnets and projecting therefromtoward the diaphragm, and a resilient pad directly interposed betweenthe magnet assembly and that face of the coil which confronts the magnetassembly and surrounding the pole piece.

References Cited in the file of this patent UNITED STATES PATENTS201,488 Bell Mar. 19, 1878 1,478,709 Gernsback Dec. 25, 1923 1,569,411Thomas a- Jan. 12, 1926 1,795,948 High Mar. 10, 1931 2,069,242 GrahamFeb. 2, 1937 2,340,122 Hansen Ian. 25, 1944 2,610,259 Roberton Sept. 9,1952 FOREIGN PATENTS 368,763 Great Britain Mar. 10, 1932 490,010 GreatBritain Aug. 4, 1938 993,438 France Oct. 31, 1951

